The pathogenic yeast Candida albicans causes debilitating and often recurring fungal infections, particularly in immune-compromised patient populations including AIDS patients. These infections are usually treated with azole antifungal drugs, and resistance is significant problem, especially in HIV-infected individuals. The major mechanisms of azole resistance include point mutations and overexpression of the target enzyme and overexpression of efflux pumps. However, all of the information concerning antifungal drug resistance has been obtained from studies of clinical isolates and laboratory constructs in culture. These resistance mechanisms have not been identified or characterized in samples taken directly from the patient. The Overall Goal of this research is to characterize the quantitative expression patterns of C. albicans resistance genes in oral samples from HIV patients in order to understand the mechanisms of resistance in vivo. The Specific Aims are: 1. To adapt quantitative RT-PCR to determine levels of expression of resistance genes in vitro in culture and in vivo in patient saliva samples. 2. To determine the levels of expression for genes associated with resistance in saliva samples containing susceptible and resistant Ca from HIV + patients. The interactions between azoles and fungal cells, and azole drug resistance, will continue to be clinically significant issues for the foreseeable future. This proposal will determine the expression levels of resistance genes in susceptible and resistant isolates taken directly from human samples in patient samples, extending the observations made in yeast cultures. These analyses will further the understanding of the interactions of antifungal drugs and the target cells in the context of the host, and may lead to improvements in diagnosis, treatment and prevention of fungal infections and resistance.